Synapse
by GloriousBlackout
Summary: Shuri works with Bucky to design a new arm, while Bucky questions whether he even deserves her help.


**A/N - It's been a long time since I've been able to write anything so I apologise if I'm a little rusty, but this idea has been stuck in my brain for a while now and pretty much demanded that I write it down. Shuri is now officially my favourite Disney princess so it was a lot of fun to write for her as well.**

 **I hope you enjoy this and any feedback is appreciated!**

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When Shuri first invites Bucky to her lab, hoping to draw up plans for a new arm, he can't quite contain the chill that grips his spine.

Any fear is baseless. He knows that well enough. Shuri and T'Challa have been unfailingly kind to him since he arrived in Wakanda, fractured in a way that likely made him a burden to fix. He spent months sleeping in her lab without coming to harm, and his new lodgings in the countryside have granted him more peace than he's had in decades. Somehow, he's content and healing despite everything that's been done to him, and for the first time in years his mind feels like his own.

That knowledge cannot stop the chill when Shuri mentions her lab. Even when she takes his hand in hers and leads the way, smiling to herself as excited cries of ' _White Wolf_ ' and ' _Princess_ ' bid them farewell, Bucky's pulse roars in his ears as old memories return unbidden. Any prior experience he has of being in a lab can be narrowed to grotesque snapshots; a scalpel removing dead flesh from his shoulder; finding cool metal where his arm once was; scientists donned in white robes as masks hide their impassive faces from view; an all-consuming grey which only falters when ice creeps into his bones.

He catches himself before the memories can overwhelm him. Forcing himself to take deep breaths, he focuses on the world around him rather than what lies behind and listens as Shuri excitedly details her ideas; pausing just long enough for him to nod or contribute when the topic draws closer to something he understands.

It hits him much later that his worry had truly been for nothing. That first session – taking place mere hours after a chill crept down his spine like a ghost – had simply been a tour of the lab, followed by a discussion of the ideas Shuri had for the arm. His prior experiences had melted away as he wandered the open space, taking in the welcoming whites and blues and clear surfaces, only to pause at the window to gaze at the dazzling blue metal buried within the mountain. The lab was warm and welcoming, and nowhere near as imposingly silent as Hydra's had been. The mountain offered a continuous hive of activity as carriages transported Vibranium from one corner to the next, and Shuri's explanations of the magnetic fields brought to mind a composer detailing their prized symphony. Bucky had understood then why children involved in the Science Outreach adored her; she could make technology and science sound like magic.

(The experience had brought even older memories back; memories of a warmly lit bunker swarmed with men and women in military dress; prototypes for weapons and shields and the Commandos' outfits on prideful display as their inventor gave Bucky a tour, his dark hair standing up in all directions and soot from a failed experiment smeared on his cheek, but his eyes still as wildly intelligent as ever)

(Bucky tried to block out the splintered memories of the last time he'd seen Howard Stark, as well as the knowledge that those intelligent brown eyes now belonged to a son who'd briefly wanted him dead)

The following visits had lost the enchantment of the first, if only because work finally needed to be done. The sessions became longer and demanded far more sitting around on his part as he was assessed and prodded, not that Bucky ever complained. Shuri had made it her mission to provide distractions while she set about designing prototypes and replacing the socket for his left shoulder (which had hurt more than she likely intended and far more than he was willing to tell her. She must have realised somehow though, for later efforts had been accompanied by much larger doses of painkillers). Her distractions included everything from American movies, to short online videos which she had to explain to him constantly, to a looped recording of T'Challa – Bucky's saviour and beloved King of Wakanda – being thrown across the room after striking his own armour. The latter had Shuri cackling madly each time it played, and by the third loop Bucky found he could not contain a smile of his own, even if it was at the expense of a man he owed his sanity to.

The replacement shoulder-joint had been securely fitted by the third session. A prototype arm had been attached an hour later, though Bucky had barely had ten minutes to enjoy having two arms again before Shuri declared it wasn't ready. He'd tried to insist it was fine, but a determined " _It's not ready yet, old man_ " had silenced him, and he'd had to watch the silver prosthetic be detached and taken back to the work-desk.

His fourth visit had been a similar affair. Shuri had taken yet another scan before spending at least two hours doing calculations and collating data for the new upgrade, talking Bucky through it all the while, only to conclude that it still wasn't complete after it had been attached for a mere five minutes. By that point Bucky knew protests would be useless. He simply nodded in agreement as she carefully detached the arm from its socket, disappointment betrayed by her furrowed brow, and promised him it would be ready next time.

He hadn't been too hopeful about that. Not because he doubted her brilliance – her improved cryo-tube and success with removing his triggers had convinced him she was probably the smartest kid in the world – but because he knew a perfectionist when he saw one. He'd said as much to T'Challa once, on the rare occasion the king had time to visit the lakeside village. The man's response had been to let out a musical laugh and utter fond nothings in Xhosa, before inviting Bucky for a walk around the lake.

" _She always did like fixing things, even when they were already perfect,"_ he'd noted as they walked, his fondness for his younger sister evident in the way his eyes crinkled with a genuine smile. " _She started drawing up plans for my suit when she was only eight. By nine she had her first prototype and by eleven I got to use her design for the first time."_

The smile had only grown, and Bucky found himself wearing one of his own at the mental image of a young Shuri poring over blueprints for the Black Panther suit and forcing her brother to try out her designs. There was no doubt in his mind that T'Challa had given her all the time in the world.

" _It was perfect from the beginning, of course. I told her as much when I returned from my mission. I thought she'd be pleased, but she only shook her head and demanded I return the suit, insisting there was still so much work to be done. She's still working on it now, I'm sure."_

She is. Bucky can see the new models in a far corner, the blueprints for further updates printed on glass displays. This fifth session lacks the distractions of the previous three – Shuri promised he could walk away with the arm this time, but she needed the utmost concentration while she attached it – so his attention has wandered. It was stolen briefly by the activities beyond the window and the intricate artwork scattered around the lab, before finally landing on T'Challa's armour.

The relative quiet seems alien after four visits consisting of comfortable noise, though not enough to elicit the chill. Shuri still has music playing in the background – a blend of traditional drums and electronic beats keeping her focused on her task – and one could not mistake his surroundings for the cold labs he'd grown used to.

Here he is free to leave as he wishes, and the scientist tending to him is not hidden behind a mask and white robes. Shuri is instead wearing a dress, the same delicate blue as the Vibranium of the mountain, and her hair is styled in an elaborate braid that keeps it away from her face, highlighting the intensity of her concentration as she connects the new arm's wiring to the socket embedded in his shoulder. Her attention is so fixed on the arm he doubts even his voice would rouse her. The only other thing able to draw her gaze away is the holographic scan projected in the centre of the lab, and even then, he'll spot her eyes darting to it for a split second before the task at hand steals her away again.

Bucky lets Shuri get on with her work and chooses to amuse himself with the hologram before him. The figure is technically him – physiological data being projected by a chip behind his ear - and though he doesn't quite understand the mechanics of it (much as Shuri had tried to simplify her explanations), looking at it is oddly satisfying. Bucky watches as synapses flare all over his body, his nerves represented by calm blue tendrils, sending signals to a spinal cord and brain which resemble lit beacons. Out of curiosity, he taps the fingers of his right hand against the table and notices signals shooting to and from the figure's spine, proving that this mess of blue light is indeed him. It's calming in a way, if he can distract himself from the more sinister blue running through his blood-vessels and embedded in his muscles. Shuri has never expressed much interest in the serum – why should she, when power-granting herbs rise from the earth and her technology can heal men faster than even the serum can manage – but that doesn't mean he appreciates the reminder of it.

There's a click to his left, followed by a spark of pain that lights up on the hologram; synthetic gold disturbing the blue. Bucky winces but otherwise remains silent. The pain is gone before it really has a chance to register anyway, though he doesn't miss Shuri's eyes darting from the scan to his face. She's learned that he isn't one to complain when he's hurting, and though the slight downturn of her lips implies she disapproves, she has the grace not to say anything. That's not a conversation he wants to have, though he's certain Steve will drag him into it one day.

Fortunately, it doesn't take long until she's done. The final connection results in a sickening pressure around the shoulder, but even that passes in an instant to be replaced with the novelty of having regrown a limb. Shuri rises to her feet to admire her handiwork, then reaches for her tablet to key in data while Bucky assesses his new arm.

The first sign that this one may remain attached longer than the others did is the design. The Vibranium has been rendered pitch-black (" _Better for camouflage," Shuri had insisted as they pored over outlines in the past_ ), but the grooves are a bright gold, tracing elegant lines across the limb's surface. He takes the opportunity to clench and unclench the fist and test the shoulder's rotation, enjoying the fluidity of the movement, and tries to tell himself the arm is part of him rather than the monstrous extension his old one had been. Shuri doesn't let him test it out for long, however. She sets the tablet aside – her work complete - and faces him with an expression that's almost frighteningly eager.

"Don't act so impressed now or you'll ruin the surprise, _Ingcuka Emhlophe,_ " she says, smirking when Bucky huffs a laugh at the nickname he'll likely never escape. "Now, close your eyes."

Bucky raises one eyebrow in question, but surmises from her expression that she isn't to be argued with. He follows her command, the inviting warmth of the lab melting away to black, and surprises himself with a bark of laughter as Shuri's now distant voice insists, "Keep them closed!"

He obeys, both eager and apprehensive to find out what the princess has up her sleeve. Knowing Shuri, it could be anything. Bucky follows her footsteps as she paces around the lab, trying to interpret clues from the shuffling and rustling of items on her desk, until the noise stops and only the footsteps and quiet music remains. She comes to a halt barely a foot away from him, yet still doesn't give permission to open his eyes. It takes a while before she even utters another word, though he can hear the unmistakable tapping of fingers on a screen which suggests she's working rather than teasing him.

"You can hold out your arms now. No peeking!" she says finally, setting her tablet on the desk with a dull 'clunk'. Bucky obeys without bothering to question her sudden fondness for mystery. The temptation to open his eyes is overwhelming – too many years of distrust bristling beneath the skin – but he likes Shuri enough not to give in and ruin her surprise.

It isn't long before he feels something brush against his right hand, and out of instinct he grabs it to assess what it is. Soft fabric is caught in his grip, and when Shuri doesn't interrupt he lets himself explore further, tracing the cloth until his fingers brush metal warmed by overhead lights. Even the fabric – while soft – has a strength to it that implies Vibranium resting between the seams, and he's toured the lab enough times to recognise a Dora's armour by touch. His expression must be rather transparent, for as soon as he acknowledges what he's feeling, the outfit is pulled away and he's left grasping air.

Not for long though. Seconds later the same fabric brushes the metal of his left hand, and the resulting sensation has him freezing in shock.

It feels… not quite the same, but he can _feel_ it. Metal fingers trace the fabric, exploring the texture of cloth mixed with Vibranium, and Bucky's breath catches in his throat at how real it seems. He reaches up to grasp the metal he'd brushed earlier and there it is; a warmth he shouldn't be able to feel; would once have thought it impossible to feel. Any care for Shuri's instructions leave him as his eyes open purely to convince himself that this isn't a trick, but she doesn't seem to mind if her grin is any indication.

She lets him take the intricate armour off her hands as she picks up the tablet again, and Bucky takes a moment to clutch it in both hands, comparing the sensation. It's not quite the same. The sensation's slightly more synthetic on the left, as though he's feeling the armour through a thin veil, but it's more than he's felt on that side in seventy years.

"Your handlers actually had an inkling of how to recreate sensation," Shuri explains as she types away, logging more data for future reference. Her face screws up slightly at the mention of his handlers, as though giving them any form of credit physically burns her, but she recovers quickly enough. "They had to connect the arm to your nervous system, otherwise you'd have no control over it. They were only ever able to simulate pressure-sense and proprioception - enough that you had control over co-ordination, but not enough to replace all you'd lost. It was advanced technology for what they had at the time, but it was intended for a weapon not for…"

She shakes her head before swiping a finger across the screen. The hologram in the centre changes to represent Bucky as he is now; his new arm represented by a veiled outline and golden tendrils blending with the blue of his own nerves as they snake up to his shoulder. "I aimed to reincorporate tactile sensation first, then I added vibration-sense and pain for normalcy's sake."

To test the latter, Bucky takes one metal finger between his right index and thumb and squeezes until the pressure melts into discomfort that forces him to stop.

"I've dialled down pain," Shuri continues, too focused on what's onscreen to notice his test. "And I've created a failsafe so that if the arm is damaged, the wires related to pain will automatically cut off. I can dial those signals down further or cut them out entirely depending on your preference. There's still time to figure out what works best."

She eventually sets the tablet aside and allows herself to bask in her handiwork. Unable to stay still much longer, Bucky gets to his feet and reaches out to touch a wall, feeling harsh rock beneath his fingertips. The ability to feel is simultaneously so alien yet so familiar he thinks he could weep, and he starts to wander the lab, letting metal fingers trace as many surfaces as he can touch. He watches black vibranium skirt across solid desks and fine glass blueprints; traces the solid surface of T'Challa's armour and the silver necklace that brings it forth at his command; he runs a hand through his hair (' _It needs a wash', he thinks absently_ ) and feels the warmth of his flesh-and-bone hand. If he closes his eyes and lets himself believe he's back home, seventy years in the past, he can pretend the arm is his own; that no trauma ever tore it from him.

He doesn't deserve this. He hasn't deserved any of the kindness he's been shown here – his hands so drenched in blood he's surprised everything he touches isn't marred by his presence.

He doesn't dare utter such thoughts again. The one time he'd voiced them to Shuri – in the midst of joyous disbelief upon realising the triggers were finally gone – she'd punched him on the arm (albeit lightly) and told him in no uncertain terms that if he said such a thing again, she'd send Okoye after him.

The joke had made him relax a little, and he'd laughed even as a tear slipped down his cheek. He'd only realised later that Shuri had taken a little too long to join in; that the concern had never quite vanished from her face.

He's wasted twenty minutes strolling around the lab when a significant absence finally makes itself evident. Bucky stops for a moment, not comprehending what's missing, until his right hand comes to rest on his scarred shoulder as though to sooth a cramp that should be there.

His old arm had been heavy. Far heavier than it should have been, but Hydra had been so obsessed with strength that they hadn't cared to fix it. Over the years, the ache that accompanied prolonged activity had become a constant companion as the muscles of his shoulder and chest dealt with strain and inflammation over and over, only for the serum to heal them before the damage could become irreparable. The Winter Soldier had dealt with it, and the ice had helped numb the pain somewhat. On longer missions it even served as something of a comfort; an anchor to remind him on some level that he was human when his mind was not strong enough to do so.

During his two years on the run it had simply been a nuisance that kept him from sleeping, and his serum ate up painkillers so quickly it eventually became useless to take them.

He'd known an arm consisting of Vibranium would be lighter. He'd lifted Steve's shield enough times to assure himself of that.

He hadn't realised it would take the pain away as well.

It takes a light touch to his right arm to remind him that he's frozen in place, hand resting against his scarred shoulder and eyes closed. He opens them with a sheepish expression that becomes guilty when he notices the quiet concern in Shuri's eyes.

"I can fix it if something's wrong," she assures him, and before he can correct her she's running back to her tablet and flicking through specs for the arm. "There might be a way to make the socket more comfortable, or I can alter the pain sensation, or simply cut it out altogether-"

"Nothing's wrong," Bucky interrupts before she can draw up plans for yet another prototype. "It's just… it doesn't _hurt_."

A laugh escapes him at that – one that could turn hysterical if he's not careful – and he finally lets go of his shoulder and absently tests the joint's range-of-movement. There's no strain or heaviness, just a comfortable weight at his side, and he can't stop his eyes from watering as the gravity of that sinks in. He closes his eyes again, focuses only on the new arm and his clear mind, and feels fully human for the first time in decades. "I'd forgotten what that felt like."

Shuri's hand stills, her work forgotten for the briefest of moments, before she catches herself and starts tapping away at the screen again. Bucky doesn't miss the flash of tension across her face though; that hint of silent rage that doesn't belong in someone so young.

"Well of course it doesn't hurt," she says finally, her brightness returning as she sends a smile his way, though he doesn't fully buy it. "What idiot thought it would be a good idea to keep you in pain?"

"Oh, there were more than a few who thought that," he says, returning to his seat and trying to reassure her with a shrug. The past is behind him after all, and he's too tired to be angry at dead men. "They're all gone now. And you really don't need to make more changes. The arm's perfect."

The compliment seems to put her at ease. She glances at half-drawn specs for what was likely another arm before closing the tab, setting the designs aside for the moment. Bucky doubts she's truly done – that as perfect as the arm feels to him, she'll have dozens of improvements lurking in her brain – but she'd promised he could take this one for a test-drive and he intends to savour that opportunity. They can't wile away their days in the lab forever; sooner or later they're going to be called to another fight and they need to be ready when that time comes.

"I'll let you try the arm for a while before I update it," Shuri promises again, to Bucky's relief. Part of him had expected her to take it off him, citing some critical flaw. "I want you to report all problems to me though, no matter how small, and _tell me_ if there's ever any pain."

He's about to protest until she raises one silencing finger, and he obeys the implied demand without thinking.

"The upgrades shouldn't be too intensive," she continues, lifting the tablet again and flicking through pages of specs with a purpose. "The current model's close to completion. The only major thing I still need to do is design-related."

That surprises him. He looks down at the elegant black and gold which he'd assumed to be final, wondering what changes Shuri could possibly want or whether she's abandoned the colour-scheme altogether. He doesn't have time to voice his queries before the tablet's thrust into his hands, and he finds himself looking down at what appears to be a child's drawing. A wolf stares back at him, its white fur traced somewhat inelegantly, but the face has the level of detail he'd have expected from Steve's sketches once upon a time. It's possible Shuri has added touches to perfect the design, but overall it's clearly the product of a child. Fondness grips him as he tries to guess which one.

"It's to replace the star from the old one," Shuri explains, a warm smile on her face as she takes a seat beside him. "I could leave it blank, of course, but that would be a waste."

He can't help but laugh at the idea of him – famed assassin and ghost story – charging into battle with a child's rendition of a wolf on his shoulder. The design promises to be small though, as small as the star had been anyway, and it's a far better notion than wearing the symbol of his oppressors.

"Fundiswa, I take it?" he asks, recognising the signature at the corner of the image. It doesn't surprise him when Shuri nods an affirmative.

The little girl is one of his regular visitors down in the village. Over time, her initial shyness around him had melted and now it was hardly unusual for her to join him as he sat by the water, looking to the forests beyond. She could talk for hours about her day and her younger brothers, not seeming to care that her companion barely uttered anything in response; what Bucky had picked up of her native Xhosa wasn't yet enough to be conversational, though T'Challa had offered to teach him the essentials.

Bucky likes Fundiswa's company. She reminds him of Becca and Shuri in many ways, especially the intelligence beyond her years and complete irreverence towards him. Their latest encounter involved her tucking an orange flower behind his ear while the sunset distracted him, only to splash water in his face and run off before he could retaliate in kind, disrupting the silence with her cries of "White Wolf!"

(He'd become familiar with those two words at least)

The incident had resulted in him laughing properly for the first time in months, even when he had to wipe water from his face and shove damp hair behind his ears. The flower had stayed in place though. He hadn't had the heart to remove it even when Shuri came to fetch him, and her eyes had lit up in amusement at the sight.

"As I said, we don't need to add it," she says, pulling him away from his memories. "But leaving it out would break a little girl's heart and I'd never forgive you."

Bucky imagines she's only half-joking, though she does join in when he laughs. He hands the tablet back to her and nods in approval, anticipating what Steve will say when he notices the addition and dreading Sam's inevitable remark. He'll need to think of a suitable comeback for the latter.

They seem to be done for this session. Shuri does a final check of the arm's mechanics, giving the hologram a once-over to ensure all connections are secure, before switching off the tablet and setting it aside. After that she carefully pulls the chip away from Bucky's ear, and they watch as the hologram stutters and fades from view. It's hard to tell how many hours they've been working. Time never flows normally down here, though he guesses that when they reach the surface, the afternoon sun will have been replaced by clear, black skies and dazzling stars.

When Shuri stands to clear away her tools and return her lab to the tidiness that greets visitors on arrival, Bucky's voice is softer than he intends when he utters "Thank you."

Shuri doesn't even look at him in response. The main indicator that she's heard him is a dismissive wave of her hand before she returns to her task; far more interested in packing away her equipment. "You say that every time I see you. There's no need."

Bucky laughs, guilty as charged, before gathering up the last of the tools from the desk and handing them to Shuri so she can lock them away. "All the same," he replies, and this time she does look his way, already preparing her retort. "I could spend the rest of my life thanking you and your brother, and it still wouldn't be enough."

The retort doesn't come. Not immediately anyway. Shuri sighs and studies him with a sincerity that's almost uncomfortable, seeing through him as clearly as she'd seen through the hologram, and the moment only passes when she turns away with a teasing smile. "Please don't do that. It would get annoying very quickly."

"Yeah, it probably would," Bucky concedes, though he has no intention of stopping for the moment. He owes more than he could ever hope to repay by this point, though he knows neither Shuri nor T'Challa will ask anything in return for their help. The knowledge of that sits heavy in his chest, even during the rare moments where he's otherwise feeling lighter than air.

Shuri, it seems, doesn't have any intention of leaving him to drown in half-buried guilt. As soon as the lab is as immaculate as it can possibly get, she grabs his left hand and steers them towards the stairs with surprising ease, leaving Bucky little choice but to follow as she leads the way.

Through a membrane comprised of metal, he can feel the warmth of her hand.

"Come on, old man. There's still so much for you to see. I have some ideas for your outfit, as well as a shield for your friend to replace that ridiculous frisbee of his..."

As she talks, he's reminded of the younger sister he left behind long ago, and his heart aches a little. Shuri's enthusiasm is contagious enough that the pain doesn't last long, however, and as she details her plans to him, he allows himself to focus on the comfortable weight at his left and the clearness of his head.

Perhaps one day he'll be able to convince himself that he deserves any of this.

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 **A/N - I'm working on the assumption that Thanos' invasion occurs before the finishing touches can be added to Bucky's shoulder if we're tying this into the movies...**

 **Thank you for reading this! I hope you enjoyed it.**


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